The present invention relates to apparatus for retaining nozzles stacked one against the other in a groove of a carrier of a turbine and particularly relates to a turbine nozzle retention apparatus for retaining the nozzles in carrier grooves at the horizontal joint faces between upper and lower carrier halves which does not interfere with radially loading the nozzles.
In turbines, for example, steam turbines, there is provided a carrier for the axially spaced, circumferential arrays of nozzles. The carrier typically includes carrier halves which extend arcuately 180xc2x0 and are secured to one another at a horizontal joint face to form a 360xc2x0 array of nozzles at each axial stage position. While various techniques have been employed to retain the nozzles within the grooves of the carrier, typically the nozzles comprise an airfoil having a radial outer dovetail-shaped base for reception in a generally correspondingly dovetail-shaped groove in the carrier. Generally, the opposite side faces of each base of the nozzles are angled relative to the axis of the turbine enabling the base to accommodate the angularity of the airfoil. When the nozzles are installed in each carrier half groove, the nozzle bases are stacked one against the other within the grooves forming a semi-circular array of nozzles. The end nozzle at each horizontal joint face, prior to securing the carrier halves to one another, projects outwardly of the joint face. Radial loading pins are also provided for each nozzle. Each pin is disposed between the base of the nozzle and the base of the groove biasing the nozzle radially inwardly. A clearance between adjacent end nozzles across the horizontal joint of the upper and lower carrier halves is necessary when the carrier halves are secured to one another. Accordingly, there is a need for a retaining device at the horizontal joint face for retaining the nozzles within the carrier half groove and which does not interfere with the radial loading of the nozzles.
In accordance with a preferred embodiment of the present invention, there is provided a turbine nozzle retention apparatus for retaining nozzles at the joint interface of each carrier half that does not interfere with but works in conjunction with the radial loading device, e.g., the radial loading pins. For example, each carrier half has a plurality of axially spaced grooves having semi-circular configurations about the carrier half. Each groove has a dovetail configuration. Nozzles having a correspondingly dovetail-shaped radially outer base are inserted into the carrier groove and stacked one against the other to form an arcuate array of nozzles. At each joint interface where a clearance between adjacent nozzles of the upper and lower carrier halves is required, each end nozzle projects beyond its associated joint face.
To retain the end nozzle in the horizontal joint face while accommodating a radial loading pin, the nozzle base of each end nozzle includes a notch formed along its radial outward face and which notch includes an abutment face extending in an axial direction. A key slot is formed in each carrier half at each joint face and lies in alignment with the notch and the abutment face. An elongated key is disposed in the notch in engagement against the abutment face of the nozzle base. A radial loading pin is disposed in a recess in the outermost wall of the carrier groove and engages the portion of the nozzle base which is not notched to provide the radial inward bias to the end nozzle. The key is secured to the carrier half and in the key slot at the joint face, for example, by peening between the joint face and the key. Alternatively, the key may be retained in the key slot by one or more screws having heads recessed below the joint interface. The key therefore prevents circumferential movement of the nozzle from the carrier groove while the radial loading pin biases the nozzle radially inwardly. It will be appreciated that the end nozzle and retainer key of the present invention is provided at at least one of two horizontal joint faces for each groove of each carrier half. Preferably, all four horizontal joint faces of the two carrier halves forming each annular groove of the carrier are provided with the nozzle retention apparatus hereof.
In a preferred embodiment according to the present invention, there is provided nozzle retention apparatus for a turbine comprising a generally semi-cylindrical nozzle carrier half for extending about an axis of the turbine and having an arcuate, radially inwardly opening, shaped groove terminating at opposite ends in respective joint faces, a plurality of nozzles for the turbine, each nozzle including an airfoil and an outer base having a shape generally corresponding to the shape of the groove and received in the groove, a key slot in one of the horizontal joint faces at one end of the groove, one of the nozzles in the groove of the carrier half at the one horizontal joint face extending circumferentially beyond the joint face and having a notch formed in the base thereof extending inwardly of the one joint face and a key in the key slot secured to the carrier half and engaging in the notch of the one nozzle to retain the nozzles in the carrier half groove.
In a further preferred embodiment according to the present invention, there is provided nozzle retention apparatus for a turbine comprising a generally semi-cylindrical nozzle carrier half for extending about an axis of the turbine and having an arcuate, radially inwardly opening dovetail-shaped groove terminating at opposite ends in respective joint faces, a plurality of nozzles for the turbine, each nozzle including an airfoil and an outer base having a dovetail shape generally corresponding to the dovetail shape of the groove and received in the dovetail-shaped groove, a key slot in one of the horizontal joint faces at one end of the groove, one of the nozzles in the groove of the carrier half at the one horizontal joint face having a notch formed in the base inwardly of the one joint face, a key in the key slot secured to the carrier half and engaging in the notch of the one nozzle to retain the nozzles in the carrier half groove and a pin engaging the one nozzle to bias the one nozzle in a radial inward direction and extending between the key and a radially inwardly facing surface along a base of the groove.